This invention relates to impellers of centrifugal blowers, and more particularly to an impeller of a centrifugal blower of the backward type having particular utility in applications for handling various types of gas and capable of achieving a high fluid flow rate, a high pressure coefficient and high efficiency.
In this type of centrifugal blowers, it has hitherto been common practice to use impellers having two dimensional blades of the backward type which have a large blade inlet width and a large blade outlet width. Generally, when attempts are made at increasing the pressure and the fluid flow rate in centrifugal blowers while keeping constant the size and the number of revolutions of the impellers, it is necessary to increase the outlet blade angle, and this results in an increase in the rate of a reduction in the relative velocity of flow in the path of flow within the impeller. More specifically, in conventional impellers, the bend of the flow from a suction port to the leading edge of each blade does not take place smoothly. Particularly, since the flow makes a sharp turn in a short distance on the shroud plate side, there is a high rate of reduction in the flow velocity locally on the shroud plate side and the flow tends to be separated from the surface of each blade. This has given rise to the problems of a reduced performance of the blowers and a production of noise in operation. However, if the distance between the suction port and the leading edge of each blade is increased and the blade inlet diameter is increased to reduce the rate of a reduction in the fluid velocity between the suction port and the blade leading edge, then the length of each blade is reduced and its area becomes small, with the result that a load per unit area of each blade becomes too high. Thus attempts hitherto made at improving the performance of the centrifugal blowers by altering the structural arrangement of the impellers as aforementioned have had the disadvantages of the flow being separated from the blade surfaces and the noise being increased.